PIV&PLIF measurement of the time-resolved velocity and temperature fields around the fins of a thermoacoustic heat exchanger in oscillatory flow conditions

A typical thermoacoustic device consists of a "stack" or "regenerator" sandwiched between the cold and hot heat exchangers, which are placed in an appropriately designed acoustic resonator. The cold and hot heat exchangers work as a heat sink and heat source, respectively, which allows the thermoacoustic energy conversion to take place in the stack. However, the fluid flow and heat transfer characteristics in such conditions are not very well understood. Most handbook data are for heat exchangers in steady flow, few relevant experiments and calculations have been done for heat exchangers in oscillatory flows. This paper investigates the velocity and temperature fields around the fins of a pair of model heat exchangers placed in a quarter wavelength standing wave resonator, using Particle Image Velocimetry (PIV) and acetone-based Planar Laser Induced Fluorescence (PLIF), respectively. The fins are kept at constant temperatures by means of resistive heating and water cooling, respectively. The velocity and temperature field distributions for the whole acoustic cycle have been obtained. The impact of the inertial effect, viscous effect and thermal effect on the time-dependent local temperature and velocity distributions perpendicular to the heat exchanger fin have been studied. Furthermore, the fact of the mutual interaction between temperature and velocity distributions provides useful information for a better understanding of the fluid flow and heat transfer processes.